1. Field of the Invention
The present invention relates to a transmitter receiver which compares the intensities of light emitted by light-emitting portions provided with light-emitting diodes and detects a change in a relative inclination angle between a transmitting side and a receiving side, and in particular, to a transmitter receiver which can shield field inflection points of the light intensity distributions of the light-emitting portions.
2. Description of the Related Art
FIG. 6 is a perspective view of a pointer 1 of a wireless type which is used as a transmitter in the input device of a computer and can be operated by hand in a space. FIG. 7 is a cross sectional view illustrating the light-emitting portion of the pointer land FIG. 8 is a front view of the light-emitting portion of the pointer 1.
The pointer 1, as shown in FIG. 8, comprises five light-emitting diodes (hereinafter referred to as LEDxe2x80x9d) 2a, 2b, 2c, 2d, and 2e built in a box-shaped housing in a line, and the LEDs emit infrared light in previously determined order to freely move a cursor on the screen of a display in response to the movement of the pointer 1.
The LED mounted in the light-emitting portion has a light-emitting directivity and, as shown in FIG. 6, a light-emitting central axis Oa of the LED 2a at the center faces the front (Z direction), where the light-emitting central axis is the direction in which the intensity of light emission is the largest, and the light-emitting central axes Ob and Oc of the LEDs 2b and 2c of the light-emitting portions formed in a pair at both ends are inclined inward (in the X direction) in the direction opposite to each other and are used to control the cursor in the right-left direction (in the X direction).
Further, the light-emitting central axes Od and Oe of the LEDs 2d and 2e of the remaining light-emitting portions formed in a pair are inclined in the up-down direction (in the Y direction) in the direction opposite to each other and are used to control the cursor in the up-down direction (in the Y direction).
In this pointer 1, as shown in FIG. 8, five LEDs 2a, 2b, 2c, 2d and 2e emit light consecutively in pairs including central LED 2a, that is, LEDs 2a+2b, LEDs 2a+2c, LEDs 2a+2d, LEDs 2a+2e, in previously predetermined order, and the consecutive light emission is repeated cyclically at predetermined intervals.
A personal computer which is made a receiver is provided with a light-receiving portion 8 and, as shown in FIG. 9, a detecting section 9 for comparing the intensity of light received by the light-receiving portion 8 to detect a change in relative inclination angle of the pointer 1 between the transmitter and the receiver.
FIG. 9 shows a state in which the pointer 1 is inclined to the X (+) side with respect to the light-receiving portion 8 provided in the receiver.
Since the light-emitting central axes Ob and Oc of the LEDs 2b and 2c arranged in the right and left sides are inclined in the X direction in the direction opposite to each other, in the state in FIG. 9, the light-emitting central axis Ob of the LED 2b is inclined in the direction of the light-receiving portion 8 and the light-emitting central axis Oc of the LED 2c is inclined in the direction away from the light-receiving portion 8. Therefore, the intensity of light received by the light-receiving portion 8 is stronger in the LEDs 2a+2b than in the LEDs 2a+2c. The detecting section 9 compares the intensities of light received by the light-receiving portions and calculates the amount of inclination of the pointer 1 in the X (+) direction, whereby the cursor on the screen of the personal computer is moved in the X (+) direction.
The inclination of the pointer 1 in the Y direction can be calculated in the same way by comparing the intensity of light emitted by the LEDs 2a+2d with the intensity of light emitted by the LEDs 2a+2e. 
FIG. 7 is a cross sectional plan view of a light-emitting portion arranged at the left end of the pointer 1.
As shown in FIG. 7, the light-emitting portion provided with the LED 2b has a holder 1a formed of transparent resin at the front of the case of the pointer 1, and the LED 2b is inserted from the back side into a projecting cover 1b integrally formed with the front of the holder 1a. The LED 2b comprises a light-emitting chip 6 arranged in the case 4 made of transparent resin and a reflecting plate 7 arranged at the back of the light-emitting chip 6.
FIG. 9 schematically shows the light intensity distributions of the light-emitting portions provided with the LEDs 2b and 2c. The light intensity distributions Lb and Lc have peaks Pb1 and Pc1 on the light-emitting central axes Ob and Oc.
In the LED 2b, the case 4 and the cover 1b function as a lens to shape light-emitting fields in the direction of the axes Ob1 and Oc1, which can enlarge the range of detection of inclination angle of the pointer 1 with respect to the Z axis and improve the quality of detection.
However, light leaking from the sides of the case 4 and the cover 1b shows field inflection portions Pb2 and Pc3 produced by reflection and refraction on the spherical surface and inclined surface of the case 4 and the cover 1b. 
The field inflection points Pb2 and Pc3 produced by the light leaking from an inclined side portion (i) that faces the direction of Z, that is, the direction of the light-receiving portion 8, because the light-emitting central axes Ob and Oc are inclined, have a great effect on the angle detection intensity distribution. For example, in the state in FIG. 9, since the light-emitting central axis Ob of the LED 2b is greatly inclined in the Z direction, the intensity of light to the Z direction ought to decrease, but the light-receiving point 8 receives light stronger than inherent light from the LED 2b under the influence of the field inflection portion Pb2 caused by light leaking from the inclined side portion (i).
Accordingly, when the detecting section 9 determines a difference in the intensity of light emission between the LED 2b and the LED 2c and calculates a relative inclination angle of the light-receiving portion 8 to the pointer 1, it calculates an inclination angle different from the actual angle because of the field inflection point Pb2. Therefore, for example, there tends to be provided the problems that when the pointer 1 is inclined gradually in the X (+) direction from the Z direction, the cursor moving to the X (+) direction on the screen is suddenly moved opposite in the X (xe2x88x92) direction or is stopped on the way.
The present invention is made so as to solve the above-mentioned conventional problems. An object of the present invention is to provide a transmitter receiver which can detect a difference in the intensity of light emission between light-emitting portions without influence of the field inflection points of the light-emitting portions.
Another object of the present invention is to provide a transmitter receiver whose member for masking the light-emitting portions is hard to deviate in position where it masks the light-emitting portions.
The present invention provides a transmitter receiver comprising: a transmitter including pairs of light-emitting portions having directivity, the light-emitting portions being arranged such that the light-emitting central axes of each pair of light-emitting portions are inclined in the directions opposite to each other in the case where the light-emitting central axis is the direction in which the intensity of light emitted by the light-emitting portion is the strongest; a receiver including a light-receiving portion that receives light emitted by the pairs of light-emitting portions; and a detecting section that compares the intensities of light received by the receiver and detects a change in the relative angle between the receiver and the transmitter, wherein a mask is provided for masking the inclined side portions of the pairs of light-emitting portions that face the light-receiving portion because the light-emitting central axes are inclined.
According to the present invention, the mask for masking the inclined side portions of the light-emitting portions can prevent an error in detection caused by a disturbance in field at the field inflection points Pb2 and Pc3 of a light intensity distribution shown in FIG. 9.
For example, the transmitter is provided with two pairs of light-emitting portions, the light-emitting central axes of one pair of light-emitting portions being inclined in the direction at right angles to the direction in which the light-emitting central axes of the other pair of light-emitting portions are inclined.
The mask can be formed of a sheet having apertures from which the light-emitting portions are exposed. In this respect, it is preferable that the side of the aperture of the mask for masking the inclined side portion of the light-emitting portion is shaped into a straight line at right angles to the direction in which the light-emitting central axis is inclined. If the side of the aperture of the mask for masking the inclined side portion of the light-emitting portion is shaped into a straight line, it can prevent the masked region of the inclined side portions from being varied when the sheet is deviated in the position.
Further, it is preferable that the side opposed to the straight side of the aperture is shaped into a curve like a circular arc, a sector or the like. If the aperture is shaped into the curve, even if the interval of neighboring light-emitting portions is narrow, the neighboring apertures of the sheet can be prevented from being connected to each other.
However, the mask is not necessarily formed of one sheet and the light-emitting portions may be provided with different masks.